In the ancient days of the world, when the boundaries between the realms of gods and giants were thin and sharp as a frost-rimed blade, the mighty Thor, son of Odin, traveled often to the frozen wastes of Jötunheimr. It was during one of these perilous journeys that the god of thunder performed a deed of both great strength and unexpected tenderness. Thor had been engaged in a brutal duel with the giant Hrungnir, a creature of stone and malice. Though Thor was victorious, shattering Hrungnir’s skull with his hammer Mjölnir, a fragment of the giant’s whetstone had lodged itself deep within Thor’s own forehead. Pain-wracked and seeking relief, Thor eventually sought out the völva Gróa, a woman of immense magical power and the wife of the hero Aurvandil the Valiant.
However, the story of how Thor came to stand before Gróa begins much earlier, in the freezing mists of the North. Thor had encountered Aurvandil in the heart of the giants' territory, where the hero had become trapped or lost amidst the crushing glaciers. Seeing a fellow warrior of worth, Thor chose not to leave him to the mercy of the frost-thursar. Instead, he placed Aurvandil into a large wicker basket and hoisted the burden onto his broad shoulders. Their path back to the safety of Midgard required them to cross the Elivágar, the eleven primordial rivers that flowed from the wellspring Hvergelmir. These were no ordinary waters; they were filled with 'eitr'—a primordial venom—that hardened into jagged ice and bit into the flesh of any who dared wade through them.
The journey across the Elivágar was a trial of endurance that would have broken any lesser being. The winds howling off the ice caps were sharp enough to flay skin, and the mist that rose from the venomous rivers was thick with the stench of the world's beginning. Thor, with the water swirling around his waist and the basket containing Aurvandil pressed against his back, forged ahead. He stepped over ice floes the size of mountains and pushed through currents that threatened to sweep even a god into the abyss. The weight of Aurvandil was nothing to the god of strength, but the cold was a different matter entirely. Even for a hero of Aurvandil's stature, the environment was lethal. As Thor waded through the deepest, coldest part of the river, one of Aurvandil’s toes slipped through the weave of the basket, exposed to the biting, venomous air of the Elivágar.
By the time Thor reached the far shore and set the basket down upon the solid earth, the damage was done. The exposed toe had frozen solid, transformed into a pale, lifeless thing by the supernatural frost. Seeing that the digit was dead and would only cause Aurvandil further pain or rot, Thor took the hero’s foot in his massive hand. With a quick, decisive snap, he broke off the frozen toe. Yet, Thor did not simply discard it. In a gesture of respect for the man he had saved, Thor took the frozen bit of flesh and bone and hurled it with all his divine might high into the northern sky. There, by the power of Thor’s will and the ancient magic inherent in the frozen river's touch, the toe was transformed. It burst into a brilliant light, becoming the star known to men as Aurvandils-tá, or 'Aurvandil’s Toe,' a beacon for travelers and a testament to the rescue.
When Thor finally returned to the halls of the living, he sought out Gróa. He stood in her dwelling, the piece of Hrungnir’s whetstone still protruding from his brow, causing him a dull, throbbing agony that no ale could dull. He asked her to sing her 'galdrar'—her magic songs—over him to loosen the stone. Gróa began her work, her voice rising in a haunting, rhythmic chant that vibrated through the air and through Thor's very bones. As she sang, the stone began to wiggle and loosen within his skull. The relief was palpable, and Thor, in his gratitude, decided to repay her by sharing glad tidings. He told her of his journey across the Elivágar, of how he had found her husband Aurvandil, and how he had carried him home safely. He pointed out the new star in the sky, explaining that it was her husband's toe, immortalized in the heavens as a sign of his safe return.
Gróa, hearing that her beloved husband was alive and coming home, was overcome with a sudden, overwhelming joy. The shock of the news broke her concentration. The intricate patterns of the spells she was weaving slipped from her mind; the ancient words of power were replaced by the simple, human emotion of relief. She stopped singing, her mind racing with the thought of Aurvandil's return. Because she ceased her chanting before the work was finished, the whetstone shard stopped moving. It settled firmly back into Thor's forehead, bonding once more with the bone. Despite his pleas and her later attempts to restart the magic, the specific flow of the ritual was lost. To this day, the shard remains in Thor's head, a reminder of the time he saved a hero but lost his cure through the very joy that news brought.